Process of plating bright zinc



Patented May 9, 1939 UNITED STATES PATENT OFFICE No Drawing. Application February 25, 1936, Serial No. 65,660

2 Claims.

This invention relates to the deposition of metal and particularly to an addition agent that is useful in the electrodeposition of zinc.

Many difliculties have been experienced in the 5 electrodeposition of zinc particularly in barrel plating in that the resulting plate lacks brightness and uniformity of color. It is highly desirable, however, to obtain a rust proofing of metal without resorting to chromium, and so it has been necessary to plate with cadmium to satisfy the demand. Cadmium, however, is not only expensive, but is scarce, and therefore, cadmium plated articles are not used except where the cadmium degree of brightness is indispensable.

An object of my invention is to provide means by which zinc may be electrodeposited on metal in such manner that the resulting plate has uniformity of color and substantially the same brightness as cadmium plate. In this connection, my invention contemplates the use of an addition agent which may be added to a standard zinc plating solution without necessitating any changes in the mechanical construction of the plating apparatus.

I have discovered that sodium thiosulphate NazSzOa, 5H2O, commonly called hypo, when added to a zinc plating bath in certain proportions produces a startling effect upon the electro deposited metal. I have found that the resulting plate not only possesses a degree of brightness that is comparable to that of cadmium, but that the plate has a uniformity of color throughout its entirely, and that the plated article may be readily buffed to a smooth bright finish. These advantages have been immediately recognized by the trade, as being a very decided advance in zinc plating, the trade being Willing to pay a substantial premium to obtain the bright zinc plated articles in lieu of those plated under the standard practice.

An additional advantage is the fact that the electrolyte has greater throwing power, thereby enabling hollow articles to be plated satisfactorily in a barrel. Moreover, the electrolyte does not 45 require ageing, and does not require replenishment as often as standard solutions.

I' have found that best results are obtained when sodium thiosulphate is added in the proportion of one-quarter A) of an ounce to one gallon of solution, and I have also found that a working range may be fixed at a minimum of onesixteenth of an ounce per gallon and a maximum of three-quarters of an ounce per gallon, this being the range, which has been used in a zinc plating bath made up as follows:

Oz./gal. Zinc cyanide, Zn(CN)2 10 Sodium cyanide (NACN) 9 Sodium hydroxide (NaOH) 10 Sodium thiosulphate A The sodium thiosulphate may either be mixed 15 with the other salts before being inserted into the bath, or may be added after the other salts are dissolved.

The above named bath will give the desired brightness of zinc plating at room temperature m with an impressed current of 200 amperes at 6 volts, and that it possesses ample throwing power to plate hollow articles'in a barrel in a satisfactory manner. The resulting plate on all articles possesses brightness that closely resembles cadmium and that is uniform in color. In addition, the plate can be readily brought to a highly lustrous finish.

I claim:

1. A method of plating bright zinc upon hollow 30 articles in a barrel comprising impressing a current in the neighborhood of 200-amperes at approximately 6 volts in a zinc cyanide solution containing alkali cyanide, alkali hydroxide and sodium thiosulphate, the sodium thiosulphate being present within the range of about one-sixteenth (1%) ounce per gallon to about three-fourth ounce per gallon to produce a bright plate.

2. A method of plating bright zinc upon hollow articles in a barrel comprising impressing current in the neighborhood of 200-amperes at approximately 6 volts in a zinc cyanide solution containing alkali cyanide, alkali hydroxide and sodium thiosulphate, the thiosulphate being present in an amount approximating one-fourth 45 ounce per gallon to produce a bright plate.

VIOLA HOFFMAN. 

